Subscribe vs. waitForMessage for a 30hz topic

edit

I would like to read a topic (which is published at ~30hz) at specific moments in the execution of my code. This Q&A shows I have 2 ways to proceed:

• waitForMessage (from here) which is a "fairly heavy operation" and requires "frequent publishing" (how heavy? how frequent?);
• subscribing and updating a class member via the subscriber's callback, and using said member directly (from the second part of this).

I went the second way but realized I don't understand how to pass-by-reference (not good enough, at least, and I have found this which is related, but isn't working), so I went with:

void MyClass::frankaStateCallback(const franka_msgs::FrankaState& msg)
{
  current_franka_state_ = msg;
}

where current_franka_state_ is of type franka_msgs::FrankaState (i.e. here) which is not the simplest/lightest of messages.

I'm therefore wondering if I should use the other way or if someone could help me with understanding how to properly use a pointer in this case.

EDIT: as per lucascoelho's request

sub_franka_states_ = nh.subscribe("franka_state_controller/franka_states", 1, &MyClass::frankaStateCallback, this);

This is in the body of the constructor (wrote it following this page), but I don't understand how the problem would lie here.